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Hey family, I have a 79 cutlass supreme I dropped a olds 455 in it . Stock overhaul with an RV cam . I will be adding a different more beefer enging later on down the road . But for now with this one Do I need to worry about frame bracing .
If the 455 has a lot of HP and torque. And if you will be driving the car hard. It will twist the frame. I found out the hard way.
If you do take the body off, than box it! Some things you can do without the boxing the frame.
Here is what I did to my 87 Cutlass below. X brace in the truck, boxed the rear control arms, tried the frame rails together by the rear bumper(solid unistrut ), Added front reinforcement brace, that really helped with the car's handling!
Not show in pictures. Add brace to the top of the shock towers in rear.
Now that I have a 656HP 562.5 lb-ft 418 cu in SBO. I come upped with a plan to beef up the frame rails to survives the new engine. Still going with bolt on steel and solid unistrut with their fittings of my own design. As I do not want to remove the body. To weld on steel, also I am not a welder.
As an aerospace engineer specializing in structures, I can tell you that those bolt-on pieces do virtually nothing to stiffen the frame. Handling might be improved because your wallet is now substantially lighter, but as far as increasing frame stiffness. forget it. Any bolt-on structural element that doesn't use ream-to-fit press-in fasteners will have slop in the bolt holes. No matter how hard you torque the bolts, friction alone will not prevent the parts from moving relative to each other. This movement prevents the bolt-on parts from contributing any meaningful stiffness. Welding the parts in place (or using hot-press rivets that fill the holes, the way the factory did) WILL result in a meaningful joint, but bolts, not so much.
The other thing I keep waiting for someone to explain to me is what, exactly is that brace in front of the front suspension supposed to be doing? The beefy welded factory crossmember is orders of magnitude more stiff than any wimpy bolt-on part, and frankly, the frame horns don't contribute to frame stiffness. They just hold up the RUBBER-MOUNTED core support and the bumper. Even worse are the bars that run parallel to the frame rails under the rockers.
The frame needs torsional and bending stiffness. The only real way to do this is with a triangulated roll cage that has bars that pick up the suspension points.
I would love to see an actual test of degrees of deflection vs ft-lbs of applied torque to the frame that validates the usefulness of these items. We do that with aerospace structures. More to the point, putting additional structural element in the same plane as the ladder frame is a great way to increase weight with little increase in stiffness. I remain skeptical of the "butt G-meter."
The fact that someone welds a bunch of tubes together doesn't make them structurally useful or efficient. There's a reason why Maserati built the "birdcage" Type 61.
Working most of my life in the commercial building business. Just have to love architects and engineers in progressive job meetings. Alway right, on till you prove them wrong. Respectfully.
Working my entire life as a structural engineer, I have to love people who don't believe math or physics. Sorry, but simply adding mass doesn't guarantee an improvement if the mass is in the wrong place.
Will this type of "bolt on" bracing improve the problem of flex? Assuming that they are placed, installed, and designed properly (which is debatable in this case)....likely will provide some improvement over doing nothing within the parameters of driving on the street.
Will they solve the problem completely? No....if you truly ran this thing hard, failure would come for sure....so they do not truly stiffen the frame, only move the failure point up slightly (again...assuming they were installed properly, in the proper location and designed properly)
Disclosure: 3 years studying mechanical engineering (didn't finish) as well as several years working in Indy Car, ARCA, and NASCAR
You all can do whatever "eyeball engineering" you want, but I've seen test data from a lot of modal tests on aerospace structures. We take great pains to use tight-tolerance fasteners (typically 0.001"-0.002" clearance between the bolt shank and the hole ID) or even press-fit fasteners when we need to incorporate a bolt-on part that is intended to increase stiffness. Failure to do so typically results in nearly zero change to the stiffness of the assembly. We also take great pains to maximize the out-of-plane section when designing a stiffness-driven structure. This is why taller I-beams deflect less under the same load. If you tried to stiffen an I-beam by making the web thicker, the weight would go up significantly faster than the stiffness increases. And trying to increase the stiffness of an I-beam with bolt-on parts is virtually worthless.
Math and physics were my best subjects in school! I loved differential equation. Static and specifications of materials classes, where some of my favorite. Just saying.
April 3rd, 2024, 05:05 PM
